A computed tomographic (CT) stereotactic system that uses the principle of bringing the reference markers and the probe holder into the CT plane of the target is described. This eliminates the need for obtaining the Z coordinate and enables one to measure directly the X and Y coordinates. The use of an are and of a rotary are carrier permits one to approach the target from any point on the skull. Off-axial reconstruction permits visualization of the trajectory in both the coronal and the sagittal planes.